The invention is directed to flat panel displays generally. More particularly, the invention is directed to an improved current supply line assembly having a uniform impedance, which is used in a flat panel display to improve the display's uniformity of luminance.
An active matrix organic light-emitting display (AMOLED) includes a plurality of electroluminescent (EL) elements. Each EL element has R, G and B organic emission layers interposed between an anode electrode and a cathode electrode. Each R, G and B emission layer emits light when a first voltage is applied to the anode electrode and a second different voltage is applied to the cathode electrode.
The anode electrodes are formed to be separated from one another in respective R, G and B unit pixels, but the cathode electrode is formed as a single planar electrode that covers a portion (or all) of the display area. A plurality of anode electrode lines supply current to the anode electrodes arranged in the R, G and B unit pixels. A current supply line assembly connected to a remote power source supplies current to the anode electrode lines.
FIG. 1 is a top view of a current supply line assembly used in a conventional active matrix organic light-emitting display. An insulating substrate 100 includes a display area 110 in which R, G and B unit pixels are arranged. A planar cathode electrode 120 is formed on a surface of the insulating substrate 100 to cover the display area 110. A supply line 121 connects the cathode electrode 120 to a drain terminal 150.
An anode wiring assembly 130 is used to supply a current to a plurality of anode electrodes located proximate the display area 110. The anode wiring assembly 130 includes a plurality of spaced apart anode electrode lines 131 connected to the anode electrodes in the display area 110, and a plurality of current supply lines to supply the current to each end of each anode electrode line 131. The current supply lines include first supply lines 132 and 133, and second supply lines 134 and 135 between the first supply lines 132 and 133 to connect the first supply lines 132 and 133. In one embodiment, supply line 132 includes ends 132a and 132b; and supply line 133 includes ends 133a and 133b. One end of each anode electrode line is connected to supply line 132. The other end of each anode electrode line is connected to supply line 133.
The current supply line assembly further includes first terminal 141 and a second terminal 142 to which a current from an external power source is supplied. One end of the third supply line 136 is connected to the first terminal 141, and the other end of the third supply line 136 is connected to the second supply line 134. Similarly, one end of the third supply line 137 is connected to the second terminal 142, and the other end of the third supply line 137 is connected to second supply line 135. One end of a A-fourth supply line 121 is connected to the terminal 150, and the other end of the fourth supply line 121 is connected to cathode electrode 120.
In use, current provided to the first and second terminals 141 and 142 flows to the anode electrode lines 131 via supply lines 136 and 137. In turn, the anode electrode lines 131 route the current to the display area 110. At display area 110, the current leaves the anode electrode lines 131 to flow through the anode electrode, the emission layer and the cathode electrode 120 of each pixel arranged in the display area 110. After leaving each pixel, the current flows via supply line 121 to the drain terminal 150.
A conventional current supply line assembly constructed as described above is configured so that an electrical resistance from a point P133 to a point P134. Such a configuration fails to maintain upper and lower symmetry and left and right symmetry or to minimize overall electrical resistance. For example, if first supply line 132 has a resistance R3, and first supply line 133 has a resistance R2, then the resistance R135 at point P135 is R135=R1+R3. Similarly, the resistance R137 at point P137 is R137=R2.
If the impedances of the supply lines that provide the current to both ends of the anode electrode line 131 are identical to each other, the resistances R135 and R137 at both ends P135 and P137 of the anode electrode line 131 are the same, resulting in R1+R3=R2. However, the impedances of the current supply lines, which provide the current via the terminal 141 to both ends of the anode electrode line 131, differ from each other. For example, the impedance of the supply line from the terminal 141 to the point P135 via the points P133 and P131 differs from the impedance of the supply line from the terminal 141 to the point P137 via the point P133 by an amount equal to the electrical resistance of supply line 134.
Likewise, the impedances of the supply lines through which current is provided to both ends of the anode electrode line 131 via the terminal 142 also differ from each other. That is, the impedance of the supply line from the terminal 142 to the point P136 via the points P134 and P132 differs from the impedance of the supply line from the terminal 142 to the point P138 via the point P134 by an amount equal to the electrical resistance of the supply line 135.
Thus, when anode wiring 130 is configured in the conventional manner, voltages of different values are applied to each end of each anode electrode line 131. For example, a different voltage is applied to the point P135 than is applied to the point P137. Similarly, a different voltage is applied to the point P136 than is applied to the point P138. Specifically, the voltages applied to the points P137 and P138 are larger than those applied to the points P135 and P136. In fact, the voltage applied to point P137 differs from the voltage applied to the point P135 by an amount equal to the electrical resistance of supply line 134. Similarly, the voltage applied to point P138 differs from the voltage applied to the point P136 by an amount equal to the electrical resistance of supply line 135.
FIG. 2 shows a chart illustrating current distribution in anode electrode lines of a conventional anode wiring assembly 130. FIG. 3 is a diagram that illustrates positions of current supply lines connected to the anode electrode lines that are referenced with respect to FIG. 2.
It is assumed that, in the anode wiring 130 of FIG. 1, a leftmost anode electrode line of the anode electrode lines 131 is L1, a center anode electrode line is L5. The anode electrode lines positioned between L1 and L5 are illustratively numbered L2, L3 and L4. It is also assumed that the position of the point P135 is X1, the position of the point P137 is X44, and the positions of points at a uniform distance between the position X1 and the position X44 are X2, X3, . . . , X43.
Under this assumption, referring to the current distribution chart shown in FIG. 2, the current value at the center anode electrode line L5 is relatively smaller than that of the outermost anode electrode line L1 due to a voltage drop resulting from the electrical resistances of the supply lines 132 and 133. Furthermore, in each of the anode electrode lines L1 to L5, a voltage applied to the position X44 is relatively higher than a voltage applied to the position X1. Consequently, the value of the current flowing around the position X44 becomes relatively larger than that flowing around the position X1. This increase in current flow is caused by the voltage drop resulting from the electrical resistances of the respective anode electrode lines L1 to L5. Consequently, it can be seen that the difference d1 between a minimum current value and a maximum current value of the anode electrode lines L1 to L5 at the position X1 is different from the difference d2 between a minimum current value and a maximum current value of the anode electrode lines L1 to L5 at the position X44. Specifically, d2 is larger than d1. Additionally, a position at which the current value in each of the anode electrode lines L1 to L5 is minimized is close to the point P135 rather than the point P137, such that the resistance value R1+R3 is larger than R2. The problem most associated with configuring an anode wiring 130 in the conventional manner is that anode electrode line assembly 131 has an asymmetrical current distribution, which creates a non-uniformity of luminance in the display area 110. Consequently, a solution is needed that provides uniformity of luminance over virtually all points of the display area 110.